Method for making a mold of an amputation stump, and molding aid for such a method

ABSTRACT

A method for making a mould of an amputation stump, in which the amputation stump is inserted into a liner of a moulding aid, the liner having a longitudinal direction and a circumference, and the liner having an expansion coupling such that when the liner is extended in the longitudinal direction, this necessarily results in a reduction of the circumference.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/078,337, filed Aug. 21, 2018, and entitled “METHOD FOR MAKING A MOLDOF AN AMPUTATION STUMP, AND MOLDING AID FOR SUCH A METHOD” which is aU.S. National Entry and claims priority to PCT International PatentApplication No. PCT/EP2017/054221, filed Feb. 23, 2017, and entitled“METHOD FOR MAKING A MOLD OF AN AMPUTATION STUMP, AND MOLDING AID FORSUCH A METHOD”, which claims priority to German Patent Application No.20 2016 001 130.9, filed Feb. 23, 2016, the entire disclosures of whichare incorporated herein by this reference.

TECHNICAL FIELD

The invention relates to a method for making a mold of an amputationstump, in which method the amputation stump is inserted into a liner ofa molding aid, said liner having a longitudinal direction and acircumference. The invention moreover relates to a molding aid for sucha method.

BACKGROUND

In prosthetics of the lower extremity, the prosthesis socket assumes thecrucial role of the interface to the body. Accordingly, making a mold ofthe amputation stump, also called the prosthetic stump, is a crucialprocedure as regards the subsequent fit of the prosthesis.

Despite advances that have been made in contactless molding methods(scanning), modern practice is dominated by making a mold of the stumpby means of plaster in order to create a negative of the stump. Besidesthe low costs, this method has the advantage that trained prosthetistscan already influence the subsequent socket shape by specificallyshaping the stump from plaster. This applies in particular when thesubsequent socket is intended to have specific loading zones. Thisadvantage is lost if the socket is intended to provide support over thecomplete surface of if inexperienced technicians carry out the moldingmethod. There has therefore been growing interest in methods which exertuniform pressure on the stump during the molding. These include themolding method proposed by the Ossur company and involving an inflatedbladder, as taught in EP 0 954 258, the sand molding method developed bythe Northwestern University of Chicago (Prosthetics and OrthoticsInternational, March 2009; 33(1): 1-9), and the molding method developedby the University of Strathclyde and involving a flexible membrane in awater tank(https://givenlimb.org/improved-casting-method-for-leg-prosthetics/).The last two methods have the additional advantage that the stump can beloaded during the molding process, which results in a socket shapetailored to the loading and which can give the user an impression of thesupport behavior as early as the molding process.

WO 2008/092617 A1 discloses a molding aid comprising a plurality ofshaped parts that are arranged to be slidable and rotatable. The shapeof the stump is intended to be able to be molded thereby. Adisadvantage, however, is that this cannot be done while the stump isloaded, and the shape is also not scannable by optical methods. Theapplicant used the “anatomical SIT-Cast” system, in which the shape ofthe stump was copied using a molding aid with a ring into which thestump is inserted. The stump is covered beforehand with a plastercompound and a rubber sleeve. Experience shows that this does notprovide optimal loading of the stump.

A disadvantage in particular of the two last-mentioned methods is that,because of their design, they are not easily transportable and are thusof little benefit in everyday clinical practice. In all three methods,it is not possible to easily influence the result of the moldingprocess. A combination with optical scanning methods, which areincreasingly used in modern prosthetics, is likewise not possible.

WO 2016/135320 A1 discloses a device for creating a plaster impressionof a limb stump, said device having a pressure vessel into which astump, preferably covered with plaster, is inserted. A uniform pressureis intended to act on the stump through the fluid. A disadvantage,however, is that subsequent shaping of the plaster or of the stump isnot possible, and the stump cannot be scanned and measured optically.

U.S. Pat. No. 7,410,350 B2 discloses a device in which an amputationstump in plaster is inserted into a container such that expanderelements, which are arranged in the container, exert a pressure on theamputation stump. This is intended to overcome the disadvantages of asolution in which a plaster-coated stump is held in a ring and is loadedby the patient after an initial hardening phase in which it is notcompletely hardened.

SUMMARY

The problem addressed by the present invention is therefore to provide amethod for making a mold of an amputation stump and a molding aid forprosthetic stumps, which exert a uniform pressure on the stump duringthe molding process, can preferably be loaded by the user during themolding process, are easy to handle and transport and permit directaccess to the surface for the purpose of reshaping during the moldingprocess or for optical scanning of the surface topography instead of thephysical molding.

The invention solves the stated problem by providing a method for makinga mold of an amputation stump, in which method the amputation stump isinserted into a liner of a molding aid, said liner having a longitudinaldirection and a circumference, said method being characterized in thatthe liner has an expansion coupling, such that a lengthening of theliner along the longitudinal direction necessarily results in areduction of the circumference.

A conventional liner or an elastic membrane known from the prior art isgenerally composed of an elastic material. When the amputation stump islocated in such a material and is loaded, for example, from above in thedirection of its distal end, this leads to an elastic deformation of theliner or of the membrane, mainly a lengthening along the longitudinalaxis. This means that the liner or the membrane is expanded in thelongitudinal axis. In the case of an elastic material, this is possiblewithout radial forces occurring. By contrast, the liner in the moldingmethod according to the present invention is such that a lengthening ofthe liner along its longitudinal axis necessarily results in a reductionof its circumference. Consequently, if the amputation stump in the lineris loaded, a lengthening of the liner along the longitudinal direction,hence also a reduction of the circumference, thus results in a forceacting radially on the stump. By virtue of the particular configurationof the liner, the amputation stump is thus loaded in the radialdirection uniformly and over the complete surface.

The amputation stump, after insertion into the liner, is preferablyloaded by the patient. The loading causes a lengthening of the linerand, by virtue of the particular configuration of the liner, thislengthening causes a reduction of the circumference and consequentlybrings about a force acting radially inward on the stump. A very goodloading situation of the stump during the molding process is thusachieved.

The amputation stump, prior to insertion into the liner, is preferablyequipped with a molding material, for example plaster, and preferablywith a release layer, in particular a release film. The molding processthen takes place by the user placing the stump, coated with the moldingmaterial and optionally the release film, into the liner and exerting atensile load on the distal end of the liner such that the linerlengthens. The placement or fitting of the stump or amputation stumpinto the liner can also be designated as insertion.

By means of the tensile force exerted on the end of the liner, and thecoupling of the expansions of the liner, the liner now completelyencloses the amputation stump and exerts a pressure on the stump in thecircumferential direction, which pressure is advantageously proportionalto the longitudinal loading of the liner.

Alternatively or in addition to this, the amputation stump can bemeasured optically after insertion into the liner. The amputation stumpis preferably loaded by the patient. Here too, the above-describedloading exerts tension on the distal end of the liner and thus generatesa pressure on the amputation stump in the circumferential direction.

After insertion of the amputation stump into the liner, the amputationstump and/or the molding material is preferably shaped in order toobtain the advantageous effects already described.

The invention also solves the stated problem by providing a molding aidfor a method described here. This molding aid therefore has theabove-described liner with the described expansion coupling. The lineradvantageously has or is made of a braided tube or a net of preferablyintersecting fibers. The fibers, in an unloaded state of the liner,advantageously run at an angle of 45° to the longitudinal direction ofthe liner. This is called a diagonal fiber run. An exact angle of 45° isnot necessary, as long as the desired coupling between the longitudinalexpansion and the reduction of the circumference is achieved. The forceexerted on the amputation stump, and caused by a lengthening of theliner along its longitudinal direction, can be adjusted via the anglebetween the fiber run and the longitudinal direction of the liner. Theflatter the fiber run, i.e. the closer the described angle comes to aright angle, the greater the radially directed force that occurs duringloading along the longitudinal direction.

The liner is advantageously held in a retaining device, preferably asecuring ring. In a preferred embodiment, the liner is held in a ringshape at its proximal end.

In order to permit the greatest possible freedom of orientation of theamputation stump, the retaining device, in particular the proximalsecuring ring, is mounted such that there is a uniform longitudinalforce on the entire circumference of the liner. Various solutions areconceivable for this purpose:

-   -   The securing ring can be cardanically mounted.    -   The securing ring can have a spherical support which is mounted        in a correspondingly shaped ring.    -   The securing ring can be mounted on at least two angled links or        leaf springs which, on account of their multi-articulation        kinematics, permit a pivoting movement of the securing ring.    -   The securing ring can permit tautening of the liner in the        fitting process, such that the liner can align itself according        to the orientation of the stump and, according to the fixing at        the proximal edge, follows the orientation of the stump.

The retaining device is preferably adjustable in height. It is thuspossible, in a particularly simple way, to deal with different heightsof patients and different lengths of amputation stumps.

For this purpose, a variable clamping device is advantageously providedfor the proximal edge of the liner. In this preferred, particularlysimple solution, the liner can be turned back at the proximal end arounda loose ring, in order then to be guided distally within the securingring. By pulling on the liner edge in the distal direction, the linercan be brought to bear on the stump while the user is standing on oneleg. Through the two-fold deflection of the liner, the latter is fixedin the securing ring and can be loaded by the user.

The liner is preferably deflected about a ring and guided back ontoitself, wherein the ring with the liner comes to bear on a retainingdevice. This particularly simple way of securing the liner permits astructurally simple molding aid that is therefore cost-effective toproduce. The retaining device is advantageously secured on a supportdevice, for example a column, and is advantageously pivotable. In thisway, the retaining device can advantageously be pivoted about thelongitudinal direction of the support device.

In a preferred embodiment, the retaining device is arranged to befoldable on the support device. In this way, it can be brought to aposition of use, in which the patient can insert his amputation stumpinto a liner arranged in the retaining device, and to a transportposition, in which the retaining device is for example folded onto thesupport device in order to reduce the required installation space. Inparticular in one of these positions, advantageously in a folded downposition corresponding to the position of use, the retaining deviceadvantageously engages in latching elements, preferably latches of thesupport device, or is clamped or wedged onto the support device. In thisway, sufficient stability is achieved and incorrect use is virtuallyexcluded.

The support device, i.e. in particular the securing ring, should bemounted such that good access is possible for a prosthetist. At the sametime, the support device is advantageously adjustable in height andexchangeable. In this way, it is possible, for example, to use differentsizes of a securing ring. In order to permit easy transport, it ishelpful if the entire molding aid can be folded together, for example inorder to be easily stowed in a workshop and to be transportable ineveryday clinical practice. In a preferred embodiment of the invention,the retaining device, in particular the securing ring, is thereforesecured in a foldable manner on a vertical column. For this purpose, forexample, a hinge and a fastenable clip can be provided around thecolumn. In a preferred solution, the retaining device generates theforces to lock itself, by means of the securing ring being loaded. Forthis purpose, the securing ring, when folded down, can engage forexample in latches in the column. With a corresponding configuration, itis also possible to generate the locking only by frictional forces,which permits a stepless height adjustment. Similarly, the column of themolding aid can be configured such that, for storage and transport, itcan be released from its securing for example on a base plate. For thispurpose, a releasable connection, for example a plug connection, can beprovided. In a further preferred embodiment, the column is connected tothe base plate via a hinge. It can be pivoted to the desired position.The working position of the column preferably forms the abutment forsuch a pivoting movement, such that the column adopts a stable,preferably vertical position during the molding process. For storage ortransport, it can be pivoted, for example, toward the base plate.

The liner, which is in particular produced from a liner material,preferably has a plurality of fibers which are arranged in the linermaterial. These fibers are preferably composed of a non-elasticmaterial. The liner can have several fiber plies, preferably two, whichhave a plurality of fibers advantageously extending parallel to eachother at least in one region in each fiber ply. As long as the fibers ofthe different fiber plies intersect each other, the desired effect ofthe coupling of the expansions can also be achieved in this way.

Additionally or alternatively to this, the fibers can also form aspiral-shaped matrix. The liner then has first fibers, which form aspiral-shaped matrix in a first circumferential direction, and secondfibers, which form a spiral-shaped matrix in a second circumferentialdirection counter to the first circumferential direction. Spiral-shapedin this case means that the respective fibers extend in preferablyseveral windings about the circumference of the amputation stump andtherefore of the liner, when the liner bears on the amputation stump.

The fibers arranged in the liner material advantageously intersect at aright angle. This applies in particular when no amputation stump islocated in the liner. This angle can be changed by the insertion of thestump and in particular by the load.

Of course, the liner can also be composed of several partial linerswhich each have only one fiber ply with only one fiber direction. As analternative to intersecting fibers, it is also possible, for example,for hexagonal nets made of non-elastic fibers to be embedded in theliner material. Of course, other nets that have the desired propertiesare also possible. This means that a lengthening of the net in onedirection necessarily leads to a shortening of the net in the otherdirection.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present invention are explained in moredetail below with reference to the attached drawings, in which:

FIGS. 1a and 1b show schematic views of a liner and of an amputationstump before and after insertion;

FIGS. 2a and 2b show schematic drawings illustrating the way in whichthe liner is secured;

FIG. 3 shows the schematic view of a molding aid with the amputationstump inserted;

FIG. 4 shows the schematic view of a molding aid in the transportposition;

FIGS. 5 to 8 show various stages of a molding method according to anillustrative embodiment of the present invention, and

FIGS. 9 and 10 show two depictions of different stages of a methodaccording to a further illustrative embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 shows schematically the function of the coupling of longitudinaland transverse expansion in the liner (2), while the prosthetic stump isbeing received. The prosthetic stump is secured on the securing ring (3)and, as is indicated in the surface texture, is made of a net or braidwith diagonally extending fiber orientation. By longitudinal deformationof the liner, there is an increased orientation of the fibers in thelongitudinal direction, which at the same time reduces the circumferenceof the liner. The deformation of the liner ceases when the stump (1) iscompletely enclosed. When the stump is subjected to a load, a uniformpressure is exerted on the stump. The liner consists of a braided tubeof yarn or monofilaments or of a net of tubular shape with a diagonalprofile of the filaments or with a hexagonal structure. Braided tubesmade of polyamide or polypropylene monofilaments are particularlyadvantageous, since these are very movable and yet form a closedsurface. The size is chosen such that the stump is completely enclosedwhen the filaments of the braided tube have an intersection angle ofapproximately 90° or when the hexagonal structure is undistorted. At thedistal end, the tube can be bound together or adhesively bonded orwelded to a flexible closure cap (9). In any case, it is recommended togenerate a smooth surface internally at the distal end by means of anelastic plate being bonded in or by means of the distal end being castwith elastomer. At the proximal end, the liner is connected to thesecuring ring (3).

FIG. 2 shows a cross-sectional view of an advantageous securing of theliner on the securing ring (3). The securing ring (3) can have a steppedconfiguration in order to provide centering for the ring (4). The liner(2) is folded about the ring (4) and guided back onto itself within thesecuring ring (3). When the liner is subjected to a load, as shown inFIG. 2B, the multiple deflection results in the ring (4) being pressedfirmly onto the securing ring (3), consequently with high frictionalforces which hold the liner safely in the securing ring as long as it isloaded. An advantage of this arrangement is that the liner can beoriented inside the ring according to the position of the lower limb.Ideally, the liner is fitted by being held taut on the stump, when thefolded-down end is pulled, and then being subjected to a load by theuser.

FIG. 3 shows a possible embodiment of the whole molding aid. The liner(2) receives the stump (1). Its proximal end is held in the securingring (3). The latter is secured on the column (5) by means of a clip(7). The axle (10) allows the securing ring (3) to be folded up onto thecolumn. When folded down, the configuration creates an abutment whichholds the securing ring in a horizontal position. At the same time, whenthe securing ring is loaded from above, strong forces act on the columnand prevent the clip from slipping along the column. In this way, thesecuring ring (3) is steplessly adjustable in height, without a lockhaving to be released for this purpose.

The column (5) is secured on the base plate (6) by means of a hinge. Inthe vertical position of the column, the position of the rotation pointof the hinge creates an abutment, which is stabilized by the securingring (3) being loaded from above. It is thus possible for the moldingaid to be used without danger of the column pivoting rearward.

FIG. 4 shows the molding aid from FIG. 3 in the folded-up state. Thecolumn (5) is here pivoted onto the underside of the base plate (6). Thesecuring ring (3) is folded against the column (5). It can be seen thatthe molding aid is very compact in this state and can be easilytransported and stowed. Its erection requires few maneuvers.

FIG. 5 shows how the amputation stump 1, which in the illustrativeembodiment shown is equipped with a modeling layer of plaster 11 and arelease film, is inserted into the liner 2. A distal edge 12 of theliner 2 is turned back. The individual fibers, through which thecoupling between longitudinal expansion and circumferential reduction isobtained in the illustrated liner 2, are not shown in FIGS. 5 to 10.

The following is shown in FIG. 6. The patient 13 stands on his intactleg, and the stump 1 with the liner 2 is inserted into the securing ring3 and is held there. The patient 13 can now exert a load on theamputation stump 1 and thereby ensures that the liner 2 is lengthened inthe longitudinal direction, i.e. from the top downward in FIG. 6. Bymeans of the coupling between longitudinal expansion and transverseexpansion, this necessarily leads to a reduction of the circumferenceand therefore to a force that acts on the amputation stump 1 and isdirected radially inward.

The situation from FIG. 6 is again shown in FIG. 7, where a furtherperson, for example a prosthetist 14, is now able to shape theamputation stump 1 in the liner 2 while the amputation stump 1 is heldin the securing ring 3. In this way, the layer of plaster 11, which islocated inside the liner 2, can be modeled and, if appropriate, shapedor reshaped. In this way, account can be taken of the individualcircumstances presented by the amputation stump 1.

FIG. 8 shows the concluding phase, in which the patient 13 stands on hisintact leg and exerts a load on the amputation stump 1 inside thesecuring ring 3. In this way, the already described force is applied bythe liner 2 to the amputation stump and the molding material of plaster11 which is located inside the liner, until the material is sufficientlyhardened to remove the liner from the securing ring 3.

FIG. 9 shows the situation in a method according to a furtherillustrative embodiment of the present invention. The patient 13 againstands on his intact leg, and the amputation stump 1 is inserted intothe liner 2. However, in contrast to FIGS. 5 to 8, there is no plaster11 arranged inside the liner between the liner 2 and the amputationstump 1. The liner is again held in the securing ring 3, but it now hasmarkings 15 which permit an optical measurement.

This optical measurement is shown in FIG. 10. The amputation stump 1 ofthe patient 13 is located in the liner 2, which has the configurationshown in FIG. 9. By means of a laser measurement device 16, as is knownin principle from the prior art, the geometric shape of the liner 2 inwhich the amputation stump 1 is located is now measuredthree-dimensionally. The data thus determined can be used to produce theprosthesis socket. The securing ring 3 is arranged on the column 5 andis preferably adjustable in height, i.e. displaceable in particularalong the longitudinal direction of the column. In a particularlypreferred embodiment, the securing ring 3 is additionally pivotabletoward the column 5 in order to be able to bring the molding aid to thetransport position shown in FIG. 5. For this purpose, it is advantageousif the base plate 6 is also pivotable relative to the column 5.

1. A method for making a mold of an amputation stump, the methodcomprising: inserting the amputation stump into a liner of a moldingaid, the liner having a longitudinal direction, a circumference, and anexpansion coupling; lengthening the liner along the longitudinaldirection to reduce the circumference, wherein the amputation stump ismeasured optically after insertion into the liner.
 2. The method asclaimed in claim 1, wherein the amputation stump, after insertion intothe liner, is loaded by the patient.
 3. The method as claimed in claim1, wherein the amputation stump, prior to insertion into the liner, isequipped with a molding material and a release layer.
 4. (canceled) 5.The method as claimed in claim 3, wherein after insertion of theamputation stump into the liner, the amputation stump and the moldingmaterial is shaped.
 6. A molding aid for use with a method for making amold of an amputation stump, the molding aid comprising: a liner forreceiving an amputation stump, the liner having a longitudinaldirection, a circumference, and an expansion coupling, the linerconfigured to reduce its circumference upon lengthening of the liner inthe longitudinal direction; and a laser measuring device for opticallymeasuring the amputation stump after insertion of the amputation stumpinto the liner.
 7. The molding aid as claimed in claim 6, wherein theliner has or is made of a braided tube or a net of intersecting fibers,wherein the fibers, in an unloaded state, enclose an angle of 45° withthe longitudinal direction of the liner.
 8. The molding aid as claimedin claim 6, wherein the liner is held in a retaining device.
 9. Themolding aid as claimed in claim 8, wherein the retaining device isadjustable in height.
 10. The molding aid as claimed in claim 9, whereinthe liner is deflected around a ring and guided back onto itself, andwherein the ring with the liner comes to bear on the retaining device.11. The molding aid as claimed in claim 8, wherein the retaining deviceis exchangeable or expandable.
 12. The molding aid as claimed in claim8, wherein the retaining device is secured on a support device.
 13. Themolding aid as claimed in claim 12, wherein the retaining device isarranged foldably on the support device, and in one position engages inlatching elements or is clamped or wedged onto the support device.
 14. Amethod for making a mold of an amputation stump, the method comprising:inserting the amputation stump into a liner of a molding aid, the linerhaving a longitudinal direction, a circumference, and an expansioncoupling; lengthening the liner in the longitudinal direction to reducethe circumference, the lengthened liner providing the mold of theamputation stump; and optically measuring the amputation stump afterinsertion into the liner.
 15. The method as claimed in claim 14, furthercomprising loading the amputation stump by the patient after insertionof the amputation stump into the liner.
 16. The method as claimed inclaim 14, further comprising, prior to insertion of the amputation stumpinto the liner, equipping the amputation stump with a molding materialand a release layer.
 17. The method as claimed in claim 16, furthercomprising shaping at least one of the amputation stump and the moldingmaterial, after insertion of the amputation stump into the liner.